In certain valve devices in which annular valve surfaces are adapted for seating on a valve seat made of resilient material, such as rubber, for cutting off flow of fluid pressure therepast, said surfaces tend to cut or bite into the resilient valve seat material, especially if the seating surface of the valve is a thin lip or rib type valve. This situation is particularly critical in a device in which the annular rib valve is formed on the end of a hollow plunger or valve stem. The thin lip or rib on the plunger, which provides effective sealing at intermediate pressures, often increases the tendency of the lip or rib to cut into the resilient valve seat, especially after many cycles of seating and unseating. This cutting may propogate until the valve lip cuts through the valve seat to a point at which effective sealing can no longer be maintained, and the valve stem itself travels an extended amount. Such a situation, because of the extended travel of the valve stem, could result in seating of the exhaust valve against the exhaust valve seat and, thereby, cause pressure to be trapped in the delivery chamber.